Embossing machines are increasingly used for producing identification cards and as a rule they are a part of a complex data processing system which frequently is directly coupled to an electronic data processing device. This occasions the requirements that such an embossing machine be electronically controlled and have a high operating speed.
In embossing machines of the type having a drum-like die head the major part of each cycle of operation is taken up by the time required for angular displacement of the die head to reach a selected position. Consequently, by reducing this setting period the greatest increase in the operating speed can be attained.
In known embossing machines, a reduction of the setting period is obtained by using a stepper motor as the driving motor. However, in order to accelerate and, above all, in order to brake relative heavy masses, a very large stepper motor has to be used. Moreover, a high electrical output is required to operate such a stepper motor. Therefore, because of economic considerations, the attainable increase in operating speed is limited.
Attempts also have been made to directly drive the die head by a direct current motor having a small armature and using the drive motor itself as a brake by means of a counter electromotive force (emf) when the selected position is approached or reached. The operating speed which can be obtained with such a scheme, however, is relatively small because the maximum braking moment is limited by the thermal conditions of the motor armature or the conditions of the commutator. Moreover, the electrical consumption for a system controlled in such a way is relatively large due to the relatively high mechanical time constant if there are oscillations. This would also consume time and would have to be avoided.